Support sharing packages in the pacman cache directory placed there without pacman2pacman
This can be related to the system PDCS (https://wiki.parabolagnulinux.org/PDCS). Now pacman2pacman uses /var/cache/pacman/pkg as the torrent data directory, so I want to share all packages in that directory (which are also in torrent pacman sync DBs). It could be done scanning for new packages placed in the directory in real-time (e.g. using inotify) by other means like direct connections to mirrors (like XferCommand set to wget or curl) or offline downloading. If this is somehow expensive the process could be run manually instead. Also, this can be useful if the pacman cache directory is shared, but using pacman2pacman on other systems could be better than connecting to shared pacman cache directories.